Not An Isolated Case
One of the most publicized cases is that of a mother, father, and daughter from Stuttgart. Back in 2018, they came back from a vacation only to leave their child at the airport.
How did this happen? As they later suggested, both parents thought that their daughter was riding with the other one as they decided to leave the airport in two different cars. Luckily, the police did a great job of finding their daughter and bringing her safely home.